1. Field of the Invention
This invention relates to an internal combustion engine electrical system, and more particularly to an internal combustion engine driven generating system which is adapted to allow an internal combustion engine to drive an A.C. generator to obtain A.C. power to be supplied to a load.
2. Description of the Prior Art
In general, such a generating system has been substituted for a commercial AC power supply. Accordingly, it is required to keep the output frequency of the generating system at a commercial frequency of 50 or 60 HZ and the output voltage at a commercial voltage of 100 V, 120 V or the like. However, a conventional internal combustion engine driven generating system is constructed to supply the output of a generator directly to a load, so that it is required to keep the rotational speed of the generator constant. This renders control of the rotational speed of the engine troublesome. Also, in the conventional generating system, when the output of a commercial frequency is to be obtained in the case that the engine and the generator are directly coupled with each other, the engine speed is limited within a predetermined range. This renders an increase in ratio between the displacement of the engine and the output of the generator highly difficult. More particularly, when output of a frequency of, for example, 50 Hz is to be obtained, the use of a generator having two poles requires to set the rotational speed of the engine at 3000 rpm; however, it is substantially impossible to design an engine which is capable of generating maximum output at such a low engine speed. Also, the use of a generator having 4 poles or more to increase the output of the generator requires that the rotational speed of an engine is further decreased due to a relationship f=PN/120 (f: frequency, P: number of poles, N: rotational speed), resulting in the design of an engine being further difficult.
There is another conventional internal combustion engine driven generating system which is constructed to connect a generator through a reducer, a belt or the like to the engine. Such construction ensures an increase in rotational speed of the engine. However, the generating system has a drawback that the rotational speed of the engine is required to be controlled within a range to avoid the variation in frequency, as in the above-described prior art generating system. Also, the provision of the reducer between the engine and the generator renders the overall construction of the generating system highly complicated, to thereby necessarily cause the system to be large-sized.
The conventional internal combustion engine driven generating system as described above has another disadvantage that when a generator which cannot adjust flux of a field system such as an A.C. magneto or permanent magnet A.C. generator is used in the generating system, it fails to compensate the variation of the output voltage due to the variation of load. Further, the permanent magnet A.C. generator has characteristics that the output voltage is decreased with an increase in load current, so that a decrease in load causes the output voltage to be increased. In particular, a substantial decrease in load at a high rotational speed causes the output voltage to be considerably increased, thus, there is a fear that a load connected to the generator is damaged.